Cable modems for remote VPN connectivity

In our last column, we discussed some requirements for remote virtual private network (VPN) access solutions.

It's a subject that is near and dear to us, first because we follow the VPN and local-loop markets closely, and second because we are in the process of establishing a VPN for our remote offices. In this column, we would like to examine cable modems as an access option.

As you recall, we proposed that a good VPN remote access solution should be able to support the following:

Static IP addresses: Some applications still require it . . . sorry.

"Always on:" You need this if you are going to facilitate IP telephony and other applications.

Sufficient bandwidth: Voice, video, encapsulation, tunneling . . . it all adds up to serious bandwidth requirements.

Keep in mind these are in addition to the more obvious requirements of performance, security and cost.

So now that we have the ground rules, let's see how cable access is able to meet the basic requirements.

Dedicated/static IP addresses. This depends on the cable service provider. Some offer static addresses, while others use dynamic addressing. Most cable providers will support either, but again, for certain applications, dedicated IP addresses are preferable. This will change only when users can be located via directory services, and we are not quite there yet.

Always on. This one is simple. Yes, cable modems provide a dedicated channel.

Bandwidth requirements. The bandwidth issue with cable modems is a little more complex and has been the subject of a great deal of debate lately.

Cable modems are capable of delivering up to 10M bit/sec if you have an Ethernet card. They are slower in the upstream direction, but that is not a major issue, especially if your traffic looks like Internet user traffic, which is mostly downstream.

Cable modem users will be happy with the bandwidth they receive . . . for now. The problem will come when more of your neighbors sign up for cable service. Much like a LAN architecture, cable modems require users to share the transmission medium.

The math is pretty simple: The more users you get, the less bandwidth available for each individual user.

Fortunately, the cable industry is aware of this issue, and there are plans to fix it. One solution is to reorganize networks as more subscribers are added so that fewer subscribers are served by a single cable head-end.

The plan looks great on paper, but it is still largely unproven. Its success will depend on the responsiveness and agility of the cable providers. In short, it has not been aggressively tested yet.

So cable modems sound great for remote access, right? They have the bandwidth, they have the coverage area, and at $40 per month, the price is certainly right. Unfortunately, cable services lack three other important requirements for VPN service: security, reliability and customer service.

If cable operators are going to compete effectively in the remote office VPN market, they are going to have to deliver a standards-based security solution. Most modem vendors, including Motorola and Nortel, currently include some form of encryption or authentication.

Several manufacturers offer 56-bit Data Encryption Standard (DES) encryption. This is adequate to keep most of your neighbors from reading your messages, but it is far weaker than the triple DES encryption that is included with most VPN gear.

The ultimate security solution must be based on standards, must be interoperable and must be transparent. To this end, some ISPs have begun to bundle full-blown VPN functionality with their cable access services. BlazeNet, an ISP that offers cable modem service, recently added VPNs to its portfolio by partnering with VPNet Technologies.

Furthermore, cable service providers will have to convince a skeptical public they are capable of meeting stringent reliability standards and telco-like levels of service.

To win converts, the cable service providers will have to offer well-reasoned service-level agreements - good ones, with teeth - that cover both network performance and customer service.

But two things are certain: 1) cable modems are here to stay, so you should seriously consider them, and 2) they are going to get better and evolve into serious business access options over time.

For now, they are cheap and surprisingly plentiful. Plan toward cable modems.

Daniel Briere is president and Christine Heckart is vice president of TeleChoice, a consultancy in Boston. They can be reached at dbriere@ telechoice.com and checkart@ telechoice.com. Eric Zines, a TeleChoice analyst, contributed to this column.